1. Field of the Invention
The present invention relates to a coating composition for lubrication of steel products on which pressing or similar working (stamping, etc.) is later performed, i.e., steel products for use in press working. More particularly, it relates to such a coating composition which is useful for preparing lubricated steel products and which exhibits improved rust-preventing properties, particularly when the lubricated steel products are coiled or stacked during storage and transportation.
Steel products for use in press working include steel sheets, for example, hot rolled pickled steel sheets, cold rolled steel sheets, plated steel sheets such as galvanized steel sheets, and stainless steel sheets, as well as steel tubes or pipes and similar shaped steel products.
2. Prior Art
When a steel sheet or tube is subjected to pressing, a lubricating oil which comprises a mineral and/or vegetable base oil and various additives has commonly been employed for many years. Such a lubricating oil is applied to the surface of the steel product to be worked prior to pressing by the user such as the operator of the press machine. In order to eliminate environmental problems encountered in the handling of the lubricating oil by a user, it is the recent trend for steel sheets and tubes to be previously coated with a lubricating organic dry film containing various lubricants. The lubricating coating is provided at an appropriate stage after the steel products are manufactured and before they are sold to users. The use of such steel sheets and pipes having a previously-formed lubricating dry coating film on the surfaces thereof (hereinafter referred to collectively as "lubricated steel products") is steadily increasing.
The coating compositions useful for forming lubricating dry films in the preparation of lubricated steel products are comprised predominantly of a film-forming resin of the drying type or bake-curing type such as an acrylic resin, epoxy resin, melamine resin, or phenolic resin, and they further contain as a lubricant one or more of a fatty acid, fatty ester, fatty acid soap, metallic soap, alcohol, polyethylene fine powder, graphite, molybdenum disulfide, fluorinated resin fine powder, and the like. These coating compositions are disclosed in Japanese Patent Laid-Open Applications Nos. 60-250099(1985), 59-204668(1984), and 57-65795(1982).
For the purpose of actual use, it is desirable that a coating composition for use in preparing lubricated steel products form a dry coating film having the following properties:
(a) lubricity which is required when the lubricated steel products are press-worked; PA1 (b) rust-preventing properties after the preparation of the lubricated steel products and before they are degreased after press working; PA1 (c) film removability with a degreasing solution; and PA1 (d) anti-block or non-sticking properties while the lubricated steel products are coiled or stacked.
Most of the above-mentioned various prior art coating compositions have formulations designed so as to improve the press-formability (lubricity) of the resulting dry coating films at the expense of rust-preventing properties. In fact, lubricated steel products coated with a prior art coating composition frequently suffer from troubles due to rusting during actual use, particularly when they are coiled or stacked during storage. Accordingly, there is still a need for a coating composition suitable for use in preparing lubricated steel products whch has improved rust-preventing properties.